Method of increasing the brilliancy of photographic pictures, and composition therefor



Patented July 19, 1938 r METHOD OF INCREASING THE BRILLIANCY 0F PHOTOGRAPHIC PICTURES, AND COM POSITION THEREFOR 7 Edith Weyde, Cologne-Niehl, (irerrnany, assignor to Agfa Ansco Corporation, Binghamton, N. Y., a corporation of New York No Drawing. Application May 17, 1934, Serial No. 726,185. In Germany May 24, 1933 7. Claims.

My present invention relates to increasing the brilliancy of photographic pictures.

One of its objects is a process of increasing the brilliancy of photographic pictures which comprises fixing the pictures in the presence of a non-toning substance capable of forming a silver salt which by reaction with sodium thio sulfate forms a soluble complex compound more slowly and with more difficulty than does silver chloride. Another object is a fixing composition containing such a substance. Further objects will be seen from the detailed specification following hereinafter.

It is already known to increase toa great extent the brilliancy of photographic pictures by slightly toning or intensifying the copies espe- I cially when they are subjected to a hot-drying process. Selenium, tellurium, gold and certain sulfur compounds which are known as toning substances, are generally employed for this purpose. These intensifying or toning processes, however, have certain drawbacks. For example, toning or intensifying cannot be carried through without more or less strongly changing the tone of the picture. Furthermore, when working a large stock of photographic papers, an additional Operation is necessary for carrying out the intensifying process. It is possible, however, to add to the fixing bath selenium salts and one or the other toning sulfur compounds, such as thiosinamine, but these baths have the drawback that they work withouthaze in the image only when adding relatively small quantities and that, for example, slight variations of the acidity of the bath already lead to a complete fogging of the white portions. All these circumstances render difficult the practical employment of the process.

I have found, that an increased brilliancy of photographic pictures, also in the case of subsequent hot-drying, may advantageously be attained by taking care that non-toning substances that is to say substances which do not react with the silver of the produced picture are present during the fixing process, which form difficultly soluble silver salts and are transformed only very slowly into soluble complex compounds with the aid of thiosulfate, that is to say which more difilcultly form a soluble complex compound with sodium thiosuliate than silver chloride. or silver bromide. The substances which enter into consideration behave in the fixing bath in the same manner as behaves a small quantity or iodine which yields with silver and thiosulfate more diiiicultly soluble complex compounds than the chloride or bromide. Probably the difiicultly soluble complex compounds form a protective layer around the sliver particles and thus protect them against the slight dissolving property of the fixing bath and against aggregation.

According to the presentsinvention an intensifying of the silver pictures does not occur, the tone of the picture is influenced only to such an extent as is possible by physical change of the grain. Since the said additional substances, in contrast with most of the toning or intensifying substances, have no tendency of forming strongly colored compounds (sulfide, selenide) with silver halide or of reducing silver halide to form metallic silver, fogging of the white portions cannot occur nor can it occur when varying within wide limits the concentration of the addition or other conditions of working.

Those of the compounds which have no deleterious effect on the emulsion, such as a fogging action, may already be incorporated in the emulsion. Many of the enumerated compounds are known as sensitizers and may be incorporated in the emulsion, however, only in such small amounts which are by far too small to increase the brilliancy of the silver imagesobtained by these emulsions. If they are added in greater quantities they cause fogging of the emulsion. That is why the compounds with sensitizing properties are not suited to be added to the emulsion, but can only be used in the processing baths.

Some of these substances may alsobe employed in the developer or in an intermediate bath (between developing and fixing) in which case-it may be assumed that in these baths a conversion of the additional substance 'is effected into its difficultly soluble silver salt which is carried with it into the fixing bath. The presence of these additional substances or their silver salts in fixing is absolutely necessary.

All substances having the above described characteristics of forming salts may be employed as additions: for example, lysalbinic acid, cystine, thiosemicarbazide, 4-ethylthiochlorobenzoic acid, 4.4-diaminothiodiphenyl'-5-sulionic acid. thioaniline, 2.2'- diaminodiphenyl disulfide, mercaptobenzthiazole, dithiocarbanilic acid, dithioaldehyde thiocyanate, phenylthiourethane, guanylthiourea, thiohydantoine, thiobenzamide, thioacetanilide, thioformaldehyde, dinitrophenylthiocyanate, ethyl-phenyl-dithiocarbamic acid, diphenylene sulfide, 5.6.7-trichloro-3-oxythionaphthene, 1-amino-i-methylaminothiosulfonic acid, triphenylthiodicyanogen-diamidine, N-phenyl-S- cresyldithiourethane, tetzamethylthiuramtetrasulfide, thiobarbituric acid, tetranitrodiphenyldisulfide, 6-ethoxy-2-aminobenzthiazole, perthiocyanic acid, phenyldithiobiazolonsulfhydrate, and the like. When employing organic sulfur compounds, theeilect consists in forming a dimcultly soluble silver salt. A formation of silver sulfide is not eflfected, since these substances are not capable of forming silver sulfide under the prevailing conditions of working.

The following examples mayillustrate the present invention which, however, is not limited thereto.

Example 1.To a fixing bath containing 200 grams of sodium thiosulfate and 20 grams of potassium metabisulfite in one liter there are added 2 grams of lysalbinic acid.

The photographic pictures with the aid of such a fixing bath are distinguished by an increased brilliancy.

Example 2.--To the above specified fixing bath there is added 0.1 gram of 2.2'-diaminodiphenyldisulfide.

Example 3.0.1 gram of 4-ethylthiochlorobenzoic acid is added t 1 liter of one of the known developers for photographic papers.

What I claim is:

1. A 'method of increasing the brilliancy of photographic silver pictures which comprises exposing a silver halide emulsion, developing the latent image produced by exposure, and fixing said developed picture in a fixing bath containing mainly thiosulfate and a relatively small amount of a compound selected from the group consisting of 4-ethyl-thiochlorobenzoic acid, 4.4-diaminothiodiphenyl-S-sulfonic acid, thioaniline, 2.2-diamino-diphenyl-disulfide, dithiocarbanilic acid, phenylthiourethane, thiobenzamide, thioacetanilide, dinitrophenylthiocyanate, ethyl-phenyl-dithiocarbamic acid, diphenylene sulfide, triphenylthiodicyanogen-diamidine. N-phenyl-S-cresyldithiourethane and tetranitrodiphenyldisulfide said compounds being capable of forming with a complex compound which is formed by thiosulfate and the small quantity of silver dissolved by the thiosulfate of the fixing bath, a colorless to weakly yellow precipitate which is less soluble in an excess of thiosulfate than is silver chloride and silver bromide.

2. A method of increasing the brilliancy. of photographic silver pictures which comprises exposing a silver halide emulsion, developing the latent image produced by exposure and fixing said developed picture in an aqueous thiosulfate solution containing per liter 0.1 gram of 2.2-diaminodiphenyl-disulfide.

3. A method of increasing the brilliancy of photographic silver pictures which comprises exposing a silver halide emulsion, developing the latent image produced by exposure in a developing bath containing per liter of developer 0.1 gram of 4-ethylthiochlorobenzoic acid, and fixing the image by treatment with a fixing bath containing sodium thiosulfate.

4. A photographic treating bath which comprises an aqueous solution containing mainly thiosulfate and a relatively small amount 01 a compound selected from the group consisting of 4-ethyl-thiochlorobenzoic acid, 4.4-diamino-thiodiphenyl-B-sulfonic acid, thoianiline, 2.2'-dlamino-diphenyl-disulfide, dithiocarbanilic a 01 d, phenylthiourethane, thiobenzamide, thioacetanilide, dinitrophenylthiocyanate, ethyl-phenyl-dithiocarbamic acid, diphenylene sulfide, triphenylthiodicyanogendiamidine, N-phenyl-S-cresyldithiourethane and tetranitrodiphenyl-disulfide. said compounds being capable of forming with a complex compound which is formed by thiosulfate and the small quantity of silver dissolved by the thiosulfate of the fixing bath, a colorless to weakly yellow precipitate which is less soluble in an excess of thiosulfate than is silver chloride and silver bromide.

5.-A composition-for fixing developed photographic silver images which comprises a solution of 780 grams of water, 200 grams of sodium thiosulphate, 20 grams of potassium metabisulfite, and 0.1 gram of 2.2-diamino-diphenyldisulfide.

6. A method of increasing the brilliancy of photographic silver pictures which comprises exposing a silver halide emulsion, developing said exposed material in an aqueous solution of mainly developing agent and a relatively small amount of an organic compound having in its molecule a divalent sulfur atom and being a member of the group consisting of 4-ethyl-thiochlorobenzoic acid, 4.4-diamino-thiodiphenyl-5-sulfonic acid, thioaniline, 2.2-diamino-diphenyl-disulfide, dithiocarbanilic acid, phenylthiourethane, thiobenzamide, thioacetanilide, dinitrophenylthiocyanate, ethyl-phenyl-dithiocarbamic acid, diphenylene sulfide, trlphenyl-thiodicyanogen-diamidine, N-phenyl-S-cresyldithiourethane and tetranitrodiphenyldisulfide said compounds being capable of forming with a complex compound which is formed by thiosulfate and the small quantity of silver dissolved by the thiosulfate of the fixing bath, a colorless to weakly yellow precipitate which is less soluble in an excess 01' thiosulfate than is silver chloride and silver bromide, and then fixing said material in an aqueous solution of a thiosulfate without washing said material between developing and fixing.

'7. A composition for developing photographic silver images which comprises an aqueous solution of a developing agent and 0.1 gram of 4- ethyl-thiochlorobenzoic acid per liter of developer.

EDITH WEYDE. 

